Address setting means for fire detectors

ABSTRACT

A fire detector assembly comprises a base ( 1 ) and a sensor ( 5 ) adapted to fit the base. The base ( 1 ) is provided with passive means, such as pins ( 6 ) or contacts arranged in a pattern to represent an address of the detector. When the sensor ( 5 ) is fitted to the base ( 1 ), reading means in the sensor reads the address code and thereby conditions the sensor to receive appropriate signals from a control unit.

This invention relates to means for improving the reliability and/orreducing the cost of fire detection systems in which fire detectors areallocated a unique address code corresponding to known locations so thata control unit may selectively communicate with individual detectors atknown locations.

In known fire alarm systems there are three methods in common use ofsetting the address of a detector.

One method is to set the address code in the detector's mounting base.The address may be set actively by altering the position of one or moreswitches connected to active electronic circuitry in the base, or byuniquely programming an electronic memory connected to such circuitry inthe base. This method has the advantage that the address code is notdisturbed if the sensor part of the detector which attaches to the baseis replaced by another sensor of the same type or of a different type.The control unit will therefore correctly correlate the address codewith the location of the detector. A disadvantage of this method is thatthe electronic circuitry contained in the mounting base may be damagedwhen high voltages are applied to system wiring for the purpose ofchecking insulation resistance. A further disadvantage is that in theevent of a fault developing in the electronic circuitry contained withina mounting base mounted on a high ceiling, the fault may not be easilyrectified without the aid of ladders or scaffolding whereas the sensormay be easily removed with devices generally known as ‘extractor poles’.Special extractor poles can be made for removing electronic assembliesfrom a base but such assemblies complicate the design of the base,introduce additional mechanical and electrical connections and so reducereliability and increase costs.

A second method is to set the address in the active sensor part of thedetector. This method has the advantage that the active circuitry, i.e.sensor electronics and the communications electronics including theaddress electronics may be incorporated into one electronics therebyreducing the cost and increasing the reliability of the detector. Themounting base need not contain any electronic components other thanwiring terminations and contact means for connecting to the sensor. Thebase may therefore be subjected to high voltages when the sensor isremoved, and, because it contains no electronics the need for access tothe base for repairs or maintenance purposes is virtually eliminated.The disadvantage of such a system is that when a sensor is removed fromits base for cleaning or maintenance it may in error be replaced by asensor from another location having a different address to that set inthe detector that was removed. In this event the control unit willattribute data from the replaced detector to an erroneous location whichmay be detrimental to the performance of the system.

A third method is to set addresses sequentially and automatically duringsystem initialisation. With this method the control unit sends anaddress code to the first detector on the detector wiring circuit. Thedetector receiving the address stores the address code in its activeelectronic circuitry and then activates a switch to connect a seconddetector into the detector wiring circuit. The control unit then sendsanother address to the second detector and the process is repeated untilall detectors have been coded with an address. This technique has thedisadvantage that detectors must be wired sequentially or fitted withfurther electronic means to identify spur wired detectors. Furthermoreeach detector must contain an electronically controlled switching meanswhich increases cost and may reduce the reliability of the systembecause the operation of detectors beyond the first detector isdependent on the correct functioning of the first detector.

This invention provides an alternative solution in that the address codeis set in the base by passive means only, the sensor having means forreading the address code when it is fitted to the base. After readingthe address code, the latter means conditions the sensor to receivesignals identified by the address code.

In a preferred embodiment of the invention, the address code is set inthe mounting base by mechanical means alone and the sensor has means forsensing the position of, or presence or absence of, the mechanicalcoding means whereby when the sensor is inserted into the base, it isable to read the settings of the mechanical address means and convertthem into an equivalent electrical code. Thus the address in the base istransferred to the sensor when the sensor is inserted into the base. Insuch an arrangement the need for electronic components in the base foraddress purposes is avoided and detectors can be interchanged withoutthe risk of inadvertently changing the address of the location in whichthe detector is installed. Thus the invention can be embodied to providethe cost advantages of having all the electronics in the sensor part ofthe detector with the reliability associated with having the addresscode set in the detector base.

In the accompanying schematic drawings:

FIGS. 1 and 2 illustrate an embodiment of the invention in respectivelydifferent stages of disassembly and assembly, and

FIG. 2A illustrates a preferred comb arrangement, and

FIGS. 3-10 illustrate a modification of the embodiment shown in FIGS. 1and 2.

As shown in FIGS. 1 and 2, a mounting base (1) is fitted with two ormore terminals (2) for terminating wiring connecting the base ( 1) witha control unit (not shown) and the base of other detectors (not shown).Terminals (2) are connected to contacts (3) which connect with contacts(4) of the sensor (5) when a sensor (5) is engaged with the base (1)thus providing means for supplying power and data from the control unitto the sensor (5). The base (1) is further fitted with a plurality ofaddress coding pins (6), the presence or absence of which defines anaddress code. By way of example only, an embodiment having provisionsfor 7 pins may be binary coded to give 128 address codes. The scope ofthe invention is not limited to the presence or absence of coding pinsbut extends to coding by position of a constant or variable number ofpins and to codes other than the binary code. The sensor (5) is fittedwith movable address code reading pins (7) which align with the addresscoding pins (6) in the base (1) when the sensor (5) is engaged with thebase (1). The offset between pins (6) and (7) seen in FIG. 1 is due tothe fact that the sensor (5) needs to be rotated through a small arc,after it has been fitted to the base, so that contacts (4) engage withcontacts (3). The pins (6) and (7) are then aligned as shown in FIG. 2.

The movable address code reading pins (7) are individually biased to afirst position by electrically conducting leaf springs (8). One end ofeach electrically conducting leaf spring is common to one end of allother electrically conducting leaf springs in mechanical contact withall other movable address coding pins. Furthermore the common end of theelectrically conducting leaf spring arrangement is further connected toa source of electrical supply, preferably by an additional electricallyconducting leaf spring (8b) not in mechanical contact with an addresscode reading pin. The inset FIG. 2a illustrates a preferred combarrangement where the leaf springs 8 extend from a common member 8a, thecomb being of a one-piece structure made of conductive material. Thesource of supply may conveniently be a conducting pad on a printedcircuit board (10).

As shown in FIG. 1, when the sensor (5) is not engaged with the base(1), the electrically conducting leaf springs (8) are biased to a firstposition by their own spring action so that the address code readingpins (7) are biased to a first position away from an insulating support(11). In this state, the free end of each electrically conducting leafspring (8) is spaced apart from a respective conducting pad (9) on aprinted circuit board (12 ) which carries the circuitry for interpretingthe pattern of electrical contacts that constitute the address. As suchcircuitry may be of conventional construction, no further description isrequired. However, when the sensor (5) is engaged with the base (1),only those address coding pins (6) which are present in the base (1)depress the address code reading pins (7) to a second position wherethey cause the free ends of the electrically conducting leaf springs (8)to make contact with the respective conducting pads (9) on the printedcircuit board (12). The presence or absence of an address coding pin (6)at each location for a pin in the base determines whether or not anelectrical contact is made in the sensor. The mechanically set addresscode is therefore translated from the base to the sensor by mechanicalmeans and thence to an electrically coded address by electro-mechanicalmeans.

Since the address coding pins (6) merely serve to deflect the leafsprings (8), they may be made of any suitable material e.g. such asplastics. Suitably, a plurality of these pins (6) are provided in looseform so that the user can select a sufficient quantity and fit them tothe base (1) in the required address code pattern. As shown in thedrawings, pins (6) and (7) are of identical construction to simplifyremanufacture and they are designed to be a snap fit into respectiveapertures in member (11) of the sensor and in a web portion (13) of thebase (1).

An advantage of using passive mechanical means, such as pins (6) to formthe address code is that the address can be simply and permanentlystored by non-electronic means. Such address means is more robust thanelectronic means and it can be easily read during operation of the firedetector whereby no electronic memory is required, nor circuitry forreading the address into memory, since the passive address can beconstantly referred to as the memory. However, there may be applicationswhere the sensor includes a memory and also appropriate circuitry forstoring an address. One such application may employ mechanical meansdefining a bar code in the base (9) and optical scanning means in thesensor (5) for reading the bar code. This, of course, would be moreexpensive than the former arrangement and it would be necessary toensure that addresses were correctly read into memory.

Various passive mechanical means may be utilised to provide the addresscode in the base. For example, besides the arrangements described above,the base may have electrical contacts for making electrical connectionswith reading means in the sensor. This arrangement would have a similaradvantage to that obtained with the use of purely mechanical addressingmeans. Alternatively, devices such as reed switches and operatingmagnets may be employed although these would be more expensive and wouldrequire means to ensure no overlap of magnetic fields.

The term passive mechanical means is therefore intended to coverdifferent kinds of devices which enable an address code to be stored ina passive mechanical way so that the address can be read only after thesensor has been fitted to the base.

FIGS. 3-10 illustrate a modification wherein the coding pins (6) for thebase (1) are provided on a removable “card” (14). The term “card” isused generally since it may be of various shapes and/or materials,although it is usually a plastic card with integral pins (6). One ormore of the pins (6) are removed by the installer prior to insertingcard (14) into a “card slot” (15) in the detector base. Slot (15)comprises guides (15a, 15b and 15c) for guiding the sides of card (14),which may be chamfered (as shown in FIG. 5), into the correct positionon the base (1) until the end of the card abuts the guide (15c). As thecard (14) is inserted, a catch (16) is initially biased away from thecard by the leading edge of the card applying pressure to a ramp (16a)formed on one side of the catch and shown in the inset FIG. 4a. Uponfurther insertion the catch engages with a hole or recess (17) (orprotrusion) in or on the card when the end of the card abuts the guide15(c). As shown in FIG. 4, the catch (16) is part of a cut-out (18) inthe base (1) that defines an arm which acts like a leaf spring. When thecard is fully inserted, it cannot be removed without manually deflectingthe catch, the catch not having a second ramp in the reverse direction.It is impossible to remove the card from the base with the sensor (5)fitted because the sensor (5) then overlies and thereby prevents accessto the catch (16). The detector may be secured to the base using lockingmeans known to those in the art to prevent unauthorised removal of thesensor and the address card. Unauthorised removal of the address cardcan be detected, when the sensor is removed because its code readingpins (17) are then no longer aligned with the address coding pins (6) inthe base (1) and this could be detected by a central control to whichthe detector assembly is fitted and an alarm, pertaining to the absenceof the sensor, could thereby be given.

Preferably a part of the address card is exposed when inserted into thebase and the exposed part marked with a number or code corresponding toaddress code carried by the coding pins.

Preferably, the address card (14) is further coded, e.g., by recesses orholes (19) so that it can only be used with a designated type ofdetector, for example, either a smoke, or a heat detector. As shown inFIG. 9, the recess (19) engages with a polarising pin or key (20) on thesensor (5) as the sensor is rotated through the small arc when it isfitted to the base. FIG. 10 shows a similar construction but where therecess 19a is in a different radial position on the card 14a to engage acorresponding pin 20a. If an attempt is made to fit a TYPE A sensor(FIG. 9) to a base fitted with a TYPE B address card (FIG. 10), or aTYPE B sensor (FIG. 10) to a base fitted with a TYPE A address card(FIG. 9), the pin (19 or 19a) would abut the edge of the card (14 or14a) thereby preventing the wrong sensor (5) from being rotated fullyinto its “card reading” position. In the event of such a misfit, theaddress will not be sensed and this will cause an alarm to be given inthe central control.

As shown in FIG. 8, the address coding pins (6) may be in the form ofknock-out or press-out “poles”, e.g., buttons which are easy to removeas a result of peripheral portions of reduced cross-section (6a and 6b)made in the address card moulding.

Preferably, the address code reading pins (7) are in the form of amembrane key pad, i.e. similar to the type of construction used inhand-held calculators. However, instead of being used as a single inputkey pad, the key pad provides a parallel address coding pin input whichis sensed in order to designate a particular fire detector. The membranekey pad may be a plastics moulding with a series of integral buttons(7a) supported by membranes (7b). Each button has a conductive contact(7c) positioned over adjacent conductive tracks (not shown) formed on aprinted circuit board (20) which is part of the sensor (5). When sensor(5) is fitted to base (1), the button (7a) is depressed by the presenceof a pin (6) whereby its contact (7c) bridges the conductive tracks tocause an appropriate signal. If a pin (6) is removed from the addresscard, then a hole FIG. 3 is positioned over the pin (7) so that itscontact (7c) remains clear of the conductive tracks. FIG. 3 is a planview of the sensor (5) showing the location of the membrane key pad (7)and also the location of contact wiper (4a) which makes electricalcontact with contact (3a) on the base (1) when the sensor is fitted tothe base.

A central control including circuitry for interrogating each detector,i.e. with respect to its address and its status, is well known to thoseskilled in the art and therefore requires no further description.

We claim:
 1. An addressable fire detector assembly for receiving addresscoded signals from a central control, said assembly comprising a baseand a sensor, said base and said sensor having means which enable themto be fitted together to form said assembly, said base having passivemeans to define an address code, the passive means being formed only bymechanical means for storing the address code, said sensor having meansfor reading said address code and for conditioning said sensor toreceive said address coded signals from said central control whereby theaddress code is read when the sensor is fitted to the base and thesensor is thereby conditioned to receive signals from the centralcontrol.
 2. An assembly according to claim 1 wherein said passive meanscomprises a plurality of elements in a particular arrangement in a givenregion, the reading means in the sensor being capable of detecting thepresence or absence of said elements in said region.
 3. An assemblyaccording to claim 2 wherein said elements are mechanical elements. 4.An assembly according to claim 3 1wherein the reading means includesswitching elements which are operated by the mechanical elements wherepresent.
 5. An assembly according to claim 4 wherein the switchingelements include a plurality of leaf springs mounted on a commonconductive member, the sensor including a printed circuit having contactpads thereon which are engaged by the leaf springs that are operated bythe mechanical elements where present.
 6. An assembly according to claim1 wherein the passive means comprise electrical contacts on said base,the reading means being provided with electrical contacts for makingrespective electrical connections with the contacts on the base andincluding circuitry which is responsive to said electrical connectionsin order to read the address code.
 7. An assembly according to claim 1wherein the passive means is arranged to represent a binary addresscode.
 8. An addressible fire detector assembly according to claim 1wherein the passive means are attached to a card-shaped member which isreceived in guides on the base, the card-shaped member having either arecess or key for cooperating with a respective key or recess on thesensor when the sensor is of a designated type to be fitted to the base,the arrangement also being such that a catch secures the member to thebase when the member is fitted to the base and that the sensor makes thecatch inaccessible when the sensor is fitted to the base.
 9. An assemblyaccording to claim 1 wherein the sensor includes a memory for storingthe address code read from the passive means.
 10. An addressible firedetector assembly according to claim 1 wherein the passive means areremovably fitted to the base either individually or collectively.
 11. Anaddressible fire detector assembly according to claim 10 wherein thepassive means are part of a member which is secured against removal fromthe base when the member has been fitted to the base.
 12. An addressiblefire detector assembly according to claim 1 wherein the base is providedwith means which cooperate with the sensor to enable only a sensor of adesignated type to be fitted to the base.
 13. An addressible firedetector assembly according to claim 12 wherein a part of said means ison a member to which the passive means are attached, said member beingremovably fitted to the base.
 14. An addressible fire detector assemblyfor receiving address coded signals from a central control, saidassembly comprising a base and a sensor having means which enable themto be fitted together to form said assembly, said base also havingmechanical means for defining a bar code, said sensor having means forreading said bar code and for conditioning said sensor to receive saidaddress coded signals.
 15. An addressible fire detector assembly forreceiving address coded signals from a central control, said assemblycomprising a base and a sensor, said base and said sensor having meanswhich enable them to be fitted together to form said assembly, said basealso having a plurality of address coding pins, said pins beingspatially disposed for physically defining an address code to identifysaid assembly, said sensor having a plurality of switchable elements,which are spatially disposed for actuation by said address coding pinswhen said sensor is fitted to said base, said sensor further includingcircuitry responsive to said switching elements for reading and storingsaid address code whereby said assembly is conditioned to respond onlyto said address code signals containing said address code defined bysaid pins.
 16. An addressible fire detector assembly according to claim15 wherein said address coding pins are provided on a card, said cardbeing removably fitted to said base, said base further including meansfor locating said card in a predetermined reading position at which saidaddress code can be read.
 17. An addressible fire detector assemblyaccording to claim 16 wherein said card is provided with a predeterminededge profile and wherein said sensor is provided with abutment means toengage the predetermined edge profile of said card when said sensor isfitted to said base, said edge profile and said abutment means beingdisposed so as to enable only a sensor of a predetermined type to befitted to said base in which said card is located in said readingposition.
 18. An addressable fire detector assembly for receivingaddress coded signals from a central control, said assembly comprising abase and a sensor, said base and said sensor having engaging surfacesconfigured to enable said base and said sensor to be fitted together toform said assembly, said base having a plurality of passive mechanicalcoding pins defining an address code, each of said plurality ofmechanical coding pins having an engaging surface, the address codebeing stored only by said passive mechanical coding pins, said sensorhaving a plurality of mechanical reading pins, each responding to saidengaging surface of a corresponding one of said plurality of mechanicalcoding pins to read said address code whereby the address code is readwhen the sensor is fitted to said base and sensor is thereby conditionedto receive signals from the central control.